WO2013171915A1

WO2013171915A1 - Piezoelectric actuator, piezoelectric vibration device, and mobile terminal

Info

Publication number: WO2013171915A1
Application number: PCT/JP2012/072201
Authority: WO
Inventors: 中村　成信
Original assignee: 京セラ株式会社
Priority date: 2012-05-15
Filing date: 2012-08-31
Publication date: 2013-11-21
Also published as: TWI520390B; JP5474262B1; KR101601750B1; TW201401591A; KR20140099563A; CN204170914U; JPWO2013171915A1

Abstract

[Problem] To provide a mobile terminal, a piezoelectric vibration device, and a piezoelectric actuator capable of stably driving for extended periods of time without a flexible wiring board bonded to a piezoelectric element separating from the piezoelectric element, even when driving for extended periods of time. [Solution] A piezoelectric actuator (1) according to an embodiment of the present invention is characterized by having: a piezoelectric element (10) which is provided with a stacked body (4) having internal electrodes (2) and piezoelectric layers (3) stacked therein, and which is provided with surface electrodes (5) on one main surface of the stacked body (4), said surface electrodes (5) being electrically connected with the internal electrodes (2); and a flexible wiring board (6) which has a portion thereof bonded above the one main surface via a conductive adhesive agent (7) including conductive particles and resin, and which is provided with a wiring conductor (61) electrically connected with the surface electrodes (5). The piezoelectric actuator (1) is further characterized in that, in a bonding area between the flexible wiring board (6) and the piezoelectric element (10), more of the conductive particles are disposed in at least a peripheral edge section (601) than in other sections.

Description

Piezoelectric actuator, piezoelectric vibration device, and portable terminal

The present invention relates to a piezoelectric vibration device, a piezoelectric actuator suitable for a mobile terminal, a piezoelectric vibration device, and a mobile terminal.

As a piezoelectric actuator, as shown in FIG. 8, a bimorph piezoelectric element 10 in which a surface electrode 104 is formed on the surface of a laminate 103 in which a plurality of internal electrodes 101 and a plurality of piezoelectric layers 102 are laminated, (See Patent Document 1) A flexible wiring board 105 is joined to the main surface of the piezoelectric element 10 with a conductive joining member 106, and the surface electrode 104 of the piezoelectric element 10 and the wiring conductor 107 of the flexible wiring board 105 are electrically connected. It is known to connect to (see Patent Document 2).

Furthermore, there is known a piezoelectric vibration device in which a central portion or one end in the length direction of a bimorph type piezoelectric element is fixed to a diaphragm (see Patent Documents 3 and 4).

Japanese Patent Laid-Open No. 2002-10393 Japanese Patent Laid-Open No. 6-14396 International Publication No. 2005/004535 JP 2006-238072 A

Here, as the conductive bonding member 106 for bonding the flexible wiring board 105 and the piezoelectric element 10, solder or a conductive adhesive has been used.

However, when solder is used as the conductive bonding member 106, the rigidity of the solder is high, so that it follows the vibration of the piezoelectric actuator due to external vibration generated on the flexible wiring board 105 or resonance of the flexible wiring board 105 itself. The abnormal vibration of the flexible wiring board 105 does not occur, causing stress concentration such as shearing or bending near the end face of the joint between the piezoelectric element 10 and the flexible wiring board 105, and the flexible wiring board 105 is There was a risk of peeling.

In addition, when simply joining with a conductive adhesive, when the piezoelectric element 10 is driven at a high speed by passing a large current, the electrical and thermal resistance value of the conductive adhesive is high. Heat generated by vibration of the conductive adhesive or Joule heat generated by the conductive adhesive itself causes thermal deterioration of the resin constituting the conductive adhesive, resulting in a decrease in bonding strength. As a result, the flexible wiring board 105 may be peeled off from the piezoelectric element 10. It was.

The present invention has been devised in view of the above-mentioned problems, and its purpose is to provide a stable for a long time without peeling from the piezoelectric element even when the flexible wiring board bonded to the piezoelectric element is driven for a long period of time. And a piezoelectric actuator, a piezoelectric vibration device, and a portable terminal to be driven.

The piezoelectric actuator of the present invention includes a piezoelectric element including a laminate in which an internal electrode and a piezoelectric layer are laminated, and a surface electrode electrically connected to the internal electrode on one main surface of the laminate, On the other hand, a part of the main surface is joined via a conductive adhesive containing conductive particles and resin, and a flexible wiring board including a wiring conductor electrically connected to the surface electrode, In the bonding region between the flexible wiring board and the piezoelectric element, at least a part of the peripheral part is provided with more conductive particles than the other parts.

The piezoelectric vibration device according to the present invention includes the piezoelectric actuator and a vibration plate bonded to the other main surface of the piezoelectric element.

The portable terminal of the present invention includes the piezoelectric actuator, an electronic circuit, a display, and a housing, and the other main surface of the piezoelectric actuator is bonded to the display or the housing. Features.

According to the present invention, it is possible to obtain a piezoelectric actuator in which the flexible wiring board does not peel from the piezoelectric element even when driven for a long time without causing abnormal vibration of the piezoelectric element.

It is a schematic perspective view which shows an example of embodiment of the piezoelectric actuator of this invention. FIG. 2A is a schematic cross-sectional view taken along line AA shown in FIG. 1B, and FIG. 2B is a partially enlarged plan perspective view of the piezoelectric actuator shown in FIG. It is a partially expanded plane perspective view which shows the other example of FIG.2 (b). 1 is a schematic perspective view schematically showing a piezoelectric vibration device according to an embodiment of the present invention. It is a schematic perspective view which shows typically the portable terminal of embodiment of this invention. FIG. 6 is a schematic sectional view taken along line AA shown in FIG. FIG. 6 is a schematic cross-sectional view taken along line BB shown in FIG. (A) is a schematic perspective view which shows an example of embodiment of the conventional piezoelectric actuator, (b) is a schematic sectional drawing cut | disconnected by the AA line shown to (a).

An example of an embodiment of a piezoelectric actuator of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic perspective view showing an example of an embodiment of the piezoelectric actuator of the present invention. FIG. 2 (a) is a schematic cross-sectional view taken along line AA shown in FIG. 1 (b). FIG. 2 is a partially enlarged plan perspective view of the piezoelectric actuator shown in FIG. 1.

A piezoelectric actuator 1 according to this embodiment shown in FIG. 1 includes a laminate 4 in which an internal electrode 2 and a piezoelectric layer 3 are laminated, and a surface electrode electrically connected to the internal electrode 2 on one main surface of the laminate 4. 5 and a wiring conductor 61 that is partly bonded on one main surface via a conductive adhesive 7 containing conductive particles and resin and electrically connected to the surface electrode 5. The conductive wiring board 6 is provided, and in the bonding region between the flexible wiring board 6 and the piezoelectric element 10, at least a part of the peripheral part 601 has more conductive particles arranged than the other parts. Features.

The laminated body 4 constituting the piezoelectric element 10 is formed by laminating the internal electrode 2 and the piezoelectric layer 3, and includes an active portion 41 in which a plurality of internal electrodes 2 overlap in the laminating direction and other inactive portions 42. For example, it is formed in a long shape. In the case of a piezoelectric actuator attached to a display or casing of a mobile terminal, the length of the laminate 4 is preferably, for example, 18 mm to 28 mm, and more preferably 22 mm to 25 mm. For example, the width of the laminate 4 is preferably 1 mm to 6 mm, and more preferably 3 mm to 4 mm. For example, the thickness of the laminate 4 is preferably 0.2 mm to 1.0 mm, and more preferably 0.4 mm to 0.8 mm.

The internal electrode 2 constituting the laminated body 4 is formed by simultaneous firing with ceramics forming the piezoelectric layer 3 and includes a first electrode 21 and a second electrode 22. For example, the first electrode 21 is a ground electrode, and the second electrode 22 is a positive electrode or a negative electrode. Piezoelectric layers 3 are alternately stacked to sandwich the piezoelectric layers 3 from above and below, and the first pole 21 and the second pole 22 are arranged in the stacking order, so that the piezoelectric body sandwiched between them. A driving voltage is applied to the layer 3. As this forming material, for example, a conductor mainly composed of silver or a silver-palladium alloy having a low reactivity with piezoelectric ceramics, or a conductor containing copper, platinum, or the like can be used. You may make it contain.

In the example shown in FIG. 1, the end portions of the first pole 21 and the second pole 22 are alternately led to a pair of side surfaces facing each other of the stacked body 4. In the case of a piezoelectric actuator attached to a display or casing of a mobile terminal, the length of the internal electrode 2 is preferably 17 mm to 25 mm, for example, and more preferably 21 mm to 24 mm. For example, the width of the internal electrode 2 is preferably 1 mm to 5 mm, and more preferably 2 mm to 4 mm. The thickness of the internal electrode 2 is preferably 0.1 to 5 μm, for example.

The piezoelectric layer 3 constituting the multilayer body 4 is formed of ceramics having piezoelectric characteristics. As such ceramics, for example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), Lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used. The thickness of one layer of the piezoelectric layer 3 is preferably set to 0.01 to 0.1 mm, for example, so as to be driven at a low voltage. In order to obtain a large flexural vibration, it is preferable to have a piezoelectric d31 constant of 200 pm / V or more.

A surface electrode 5 electrically connected to the internal electrode 2 is provided on one main surface of the laminate 4. The surface electrode 5 in the form shown in FIG. 1 includes a first surface electrode 51 having a large area, a second surface electrode 52 having a small area, and a third surface electrode 53. For example, the first surface electrode 51 is electrically connected to the internal electrode 2 to be the first electrode 21, and the second surface electrode 52 is the internal electrode to be the second electrode 22 disposed on one main surface side. 2 and the third surface electrode 53 is electrically connected to the internal electrode 2 serving as the second electrode 22 disposed on the other main surface side. In the case of a piezoelectric actuator attached to a display or casing of a portable terminal, the length of the first surface electrode 51 is preferably, for example, 17 mm to 23 mm, and more preferably 19 mm to 21 mm. The width of the first surface electrode 51 is preferably 1 mm to 5 mm, for example, and more preferably 2 mm to 4 mm. The lengths of the second surface electrode 52 and the third surface electrode 53 are preferably 1 mm to 3 mm, for example. The widths of the second surface electrode 52 and the third surface electrode 53 are preferably 0.5 mm to 1.5 mm, for example.

The piezoelectric actuator 1 has a flexible wiring board 6 partially bonded to one main surface of a laminate 4 constituting the piezoelectric element 10 via a conductive adhesive 7 made of conductive particles and resin. Yes.

The flexible wiring board 6 includes a wiring conductor 61, and a part of the flexible wiring board 6 is formed of the laminate 4 so that the surface electrode 5 and the wiring conductor 61 are electrically connected via the conductive adhesive 7. On the other hand, it is joined to the main surface.

The flexible wiring board 6 is a flexible printed wiring board in which, for example, two wiring conductors 61 are embedded in a resin film, and a connector (not shown) for connecting to an external circuit is connected to one end. Yes.

Examples of the conductive adhesive 7 include metal powders such as silver powder and gold powder in a resin having a low elastic modulus (Young's modulus) such as polyimide, polyamideimide, silicone rubber, and synthetic rubber, and Au plating on a resin ball. Conductive particles made of conductive coating or the like are dispersed. Thereby, compared with solder, the stress produced by vibration can be reduced. More preferably, the conductive adhesive 7 is preferably an anisotropic conductive material. The anisotropic conductive material is composed of conductive particles responsible for electrical bonding and a resin adhesive responsible for adhesion. Since this anisotropic conductive material can conduct in the thickness direction and insulate in the in-plane direction, even in narrow-pitch wiring, there is no electrical short between surface electrodes of different polarities, and flexible wiring A connection part with the board | substrate 6 can be made compact.

Further, in the bonding region between the flexible wiring board 6 and the piezoelectric element 10, at least a part of the peripheral part 601 is provided with more conductive particles than the other parts. Here, the bonding region is a region occupied by the conductive adhesive 7, and the peripheral edge portion 601 of the bonding region means a region within 0.4 mm from the end surface. Further, the fact that more conductive particles are arranged in a part of the peripheral part 601 than in other parts means that the peripheral part 601 is obtained when the flexible wiring substrate 6 is peeled off and the surface of the conductive adhesive 7 is observed with an electron microscope. This means that the proportion of conductive particles in a part of the unit area per unit area is larger than that of the other part.

As described above, since the conductive particles are disposed more than the other parts in at least a part of the peripheral part 601 of the joining region between the flexible wiring board 6 and the piezoelectric element 10, the thermal conductivity of this part is improved. Therefore, the conductive adhesive 7 is configured to promote heat conduction and diffusion of the heat generated by the vibration of the piezoelectric element 10 and Joule heat of the conductive adhesive 7 even when driven at a high speed by passing a large current. The problem that the resin is thermally deteriorated and the flexible wiring board 6 is peeled off from the piezoelectric element 10 can be greatly reduced.

In addition, by arranging a large number of conductive particles in at least a part of the peripheral portion 601, shearing and tensile stress concentration is reduced due to rotation of the conductive particles and a low Young's modulus. Therefore, the conductive adhesive 7 is prevented from cracking from this portion. In particular, when a force is applied in the direction in which the flexible wiring board 6 is connected to the outside, a large shearing or tensile stress is concentrated at the base of the joint portion of the flexible wiring board 6. Therefore, the concentration of shear stress can be particularly suppressed by the rotation of the conductive particles of the conductive adhesive 7, and there is no risk that the flexible wiring board 6 is peeled off due to cracks at the base of the joint. . It is preferable that at least a part of the peripheral portion 601 having more conductive particles than other portions is the entire periphery of the peripheral portion 601.

In addition, it is preferable that at least a part of the peripheral portion 601 in which many conductive particles are arranged, for example, the number or ratio of the conductive particles is 5 to 20% larger than other parts. This ratio can be obtained by removing the flexible wiring board 6 and observing it with an electron microscope.

Further, as shown in FIG. 3, since the part is in a region between the outer periphery of one main surface of the piezoelectric element 10 and the surface electrode 5, the low Young's modulus of the resin and the rotation of many conductive particles are external. It is possible to reduce stress generated by vibration that does not follow the actuator such as vibration and resonance of the flexible wiring board 6 itself, and to reduce the amplitude of such vibration that the viscoelasticity of the resin does not follow.

Further, the thickness of the conductive adhesive 7 bonded in the region between the outer periphery of the one main surface of the piezoelectric element 10 and the surface electrode 5 is such that the surface electrode 5 and the wiring conductor 61 are electrically connected to face each other. Although the thermal resistance increases because it is thicker than the thickness of the conductive adhesive 7, a connection with a thermal conductivity function that suppresses an increase in thermal resistance by arranging a large number of conductive particles having high thermal conductivity in this region is used. be able to. As a result, heat generated by vibration of the piezoelectric element 10 and Joule heat of the conductive adhesive 7 itself can be conducted and diffused, and cracking due to deterioration of the resin constituting the conductive adhesive 7 can be reduced.

In the above configuration, when the conductive adhesive 7 is an anisotropic conductive material containing, for example, gold-plated resin balls as conductive particles, the surface electrode 5 and the wiring conductor 61 overlap in a plan view. The conductive particles constituting the conductive adhesive 7 electrically connect the surface electrode 5 and the wiring conductor 61, and the conductive particles are not joined to each other. In other regions, the piezoelectric element 10 and the wiring conductor are connected. It is easy to form a connection form in which conductive particles that are not connected to either 61 or only connected to either one exist mainly. With such a connection form, it is possible to suppress the stress concentration of shear and tension while maintaining high heat conduction as described above. It may be a joining process.

As described above, in order to effectively improve heat conduction and reduce stress concentration, it is preferable that the conductive particles not connected to either the piezoelectric element 10 or the wiring conductor 61 be 70% or more of the whole.

Further, by making the other main surface of the piezoelectric element 10 flat, for example, when the other main surface is bonded to an object to be vibrated (for example, a vibration plate to be described later), it is integrated with the object to be vibrated. As a result, bending vibration is easily generated, and the efficiency of bending vibration can be improved as a whole.

The piezoelectric actuator 1 shown in FIG. 1 is a so-called bimorph type piezoelectric actuator that receives an electric signal from the surface electrode 5 and vibrates and vibrates so that one main surface and the other main surface are bent surfaces. However, the piezoelectric actuator of the present invention is not limited to the bimorph type, and may be a unimorph type. For example, by joining (bonding) the other principal surface of the piezoelectric actuator to a diaphragm described later, It can be bent and vibrated.

Next, a method for manufacturing the piezoelectric actuator 1 according to this embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 3 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced using this ceramic slurry by using tape molding methods, such as a doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

Next, a conductive paste to be the internal electrode 2 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium alloy metal powder. This conductive paste is applied on the ceramic green sheet in the pattern of the internal electrode 2 using a screen printing method. Further, a plurality of ceramic green sheets printed with this conductive paste are laminated, subjected to a binder removal treatment at a predetermined temperature, fired at a temperature of 900 to 1200 ° C., and then subjected to a predetermined grinding using a surface grinder or the like. By performing a grinding process so as to obtain a shape, a laminated body 4 including the internal electrodes 2 and the piezoelectric body layers 3 that are alternately laminated is manufactured.

The laminate 4 is not limited to the one produced by the above manufacturing method, and any production method can be used as long as the laminate 4 formed by laminating a plurality of internal electrodes 2 and piezoelectric layers 3 can be produced. It may be produced.

Thereafter, a silver glass-containing conductive paste prepared by adding a binder, a plasticizer, and a solvent to a mixture of conductive particles mainly composed of silver and glass is used to form a main surface of the laminate 4 in a pattern of the surface electrode 5. After the surface is printed by screen printing or the like and dried, a baking process is performed at a temperature of 650 to 750 ° C. to form the surface electrode 5.

When the surface electrode 5 and the internal electrode 2 are electrically connected, a via that penetrates the piezoelectric layer 3 may be formed or connected, or a side electrode may be formed on the side surface of the multilayer body 4. It may be produced by any manufacturing method.

Next, the flexible wiring board 6 is connected and fixed (bonded) to the piezoelectric element 10 using the conductive adhesive 7.

First, a conductive adhesive paste is applied and formed on a predetermined position of the piezoelectric element 10 using a technique such as screen printing. Thereafter, the conductive adhesive paste is cured with the flexible wiring board 6 in contact with the flexible wiring board 6, thereby connecting and fixing the flexible wiring board 6 to the piezoelectric element 10. The conductive adhesive paste may be applied and formed on the flexible wiring board 6 side.

When the resin constituting the conductive adhesive 7 is made of a thermoplastic resin, the conductive adhesive is applied to a predetermined position of the piezoelectric element 10 or the flexible wiring board 6, and then the piezoelectric element 10 and the flexible wiring board 6 are formed. Is heated and pressed in a state of being in contact with the conductive adhesive, so that the thermoplastic resin is softened and fluidized and then returned to room temperature, so that the thermoplastic resin is cured again, and the flexible wiring board 6 becomes a piezoelectric element. Connection fixed to 10.

Here, in order to ensure that many conductive particles constituting the conductive adhesive 7 are arranged in the peripheral portion of the region of the flexible wiring board 6 that overlaps the piezoelectric element 10 in plan view, the content of the conductive particles is further increased. A large amount of conductive adhesive paste may be prepared, and a conductive adhesive paste having a high content of conductive particles may be applied and formed on the periphery.

In particular, when an anisotropic conductive member is used as the conductive bonding member 7, it is necessary to control the amount of pressurization so that adjacent conductive particles do not come into contact with each other.

In the above description, the method of applying and forming the conductive adhesive 7 on the piezoelectric element 10 or the flexible wiring board 6 has been described. However, the sheet of the conductive adhesive 7 formed in advance in a sheet shape is connected to the piezoelectric element 10 and the flexible wiring. You may heat-press and join in the state pinched | interposed between the board | substrates 6.

The piezoelectric vibration device of the present invention has a piezoelectric actuator 1 and a vibration plate 81 joined to the other main surface of the piezoelectric actuator 1 as shown in FIG.

The diaphragm 81 has a rectangular thin plate shape. The vibration plate 81 can be preferably formed using a material having high rigidity and elasticity such as acrylic resin or glass. Further, the thickness of the diaphragm 81 is set to 0.4 mm to 1.5 mm, for example.

The diaphragm 81 is joined to the other main surface of the piezoelectric actuator 1 via a joining member 82. The entire surface of the other main surface may be bonded to the diaphragm 81 via the bonding member 82, or substantially the entire surface may be bonded.

The joining member 82 has a film shape. Further, the joining member 82 is formed of a material that is softer and more easily deformed than the diaphragm 81, and has a smaller elastic modulus and rigidity such as Young's modulus, rigidity, and bulk modulus than the diaphragm 81. That is, the joining member 82 is deformable and deforms more greatly than the diaphragm 81 when the same force is applied. Then, the other main surface (main surface on the −z direction side in the drawing) of the piezoelectric actuator 1 is fixed to the one main surface (main surface on the + z direction side in the drawing) of the bonding member 82 as a whole. A part of one main surface (main surface on the + z direction side in the drawing) of the diaphragm 81 is fixed to the other main surface (main surface on the −z direction side in the drawing).

The joining member 82 may be a single member or a composite composed of several members. As such a joining member 82, for example, a double-sided tape in which a pressure-sensitive adhesive is attached to both surfaces of a substrate made of a nonwoven fabric or the like, various elastic adhesives which are adhesives having elasticity, and the like can be suitably used. The thickness of the joining member 82 is desirably larger than the amplitude of the flexural vibration of the piezoelectric actuator 1, but if it is too thick, the vibration is attenuated, so it is set to 0.1 mm to 0.6 mm, for example. However, in the piezoelectric vibration device of the present invention, the material of the bonding member 82 is not limited, and the bonding member 82 may be formed of a material that is harder and less deformable than the vibration plate 81. In some cases, a configuration without the joining member 82 may be used.

The piezoelectric vibration device of this example having such a configuration functions as a piezoelectric vibration device that causes the piezoelectric actuator 1 to bend and vibrate by applying an electric signal, thereby vibrating the vibration plate 81. Note that the other end in the length direction of the diaphragm 81 (the end in the −y direction in the figure, the peripheral edge of the diaphragm 81, and the like) may be supported by a support member (not shown).

Since the piezoelectric vibration device of this example is configured using the piezoelectric actuator 1 in which generation of unnecessary vibration is reduced, the piezoelectric vibration device in which generation of unnecessary vibration is reduced can be obtained.

Further, in the piezoelectric vibration device of this example, the vibration plate 81 is joined to the other flat main surface of the piezoelectric actuator 1. Thereby, a piezoelectric vibration device in which the piezoelectric actuator 1 and the vibration plate 81 are firmly joined can be obtained.

As shown in FIGS. 5 to 7, the mobile terminal of the present invention includes the piezoelectric actuator 1, an electronic circuit (not shown), a display 91, and a housing 92, and the other side of the piezoelectric actuator 1. The main surface is joined to the housing 92. 5 is a schematic perspective view schematically showing the portable terminal of the present invention, FIG. 6 is a schematic cross-sectional view taken along the line AA shown in FIG. 5, and FIG. 7 is a line BB shown in FIG. It is the schematic sectional drawing cut | disconnected by.

Here, it is preferable that the piezoelectric actuator 1 and the housing 92 are joined using a deformable joining member. That is, in FIG. 6 and FIG. 7, the joining member 82 is a deformable joining member.

By joining the piezoelectric actuator 1 and the housing 92 with the deformable joining member 82, when the vibration is transmitted from the piezoelectric actuator 1, the deformable joining member 82 is deformed more greatly than the housing 92.

At this time, since the anti-phase vibration reflected from the casing 92 can be mitigated by the deformable joining member 82, the piezoelectric actuator 1 transmits strong vibration to the casing 92 without being influenced by the surrounding vibration. Can be made.

In particular, since at least a part of the joining member 82 is formed of a viscoelastic body, strong vibration from the piezoelectric actuator 1 is transmitted to the housing 92, while weak vibration reflected from the housing 92 is transmitted to the joining member 82. It is preferable in that it can be absorbed. For example, a double-sided tape in which a pressure-sensitive adhesive is attached to both surfaces of a base material made of a nonwoven fabric or the like, or a joining member including an adhesive having elasticity can be used, and the thickness thereof is, for example, 10 μm to 2000 μm Can be used.

In this example, the piezoelectric actuator 1 is attached to a part of the casing 92 that becomes the cover of the display 91, and a part of the casing 92 functions as the diaphragm 922.

In this example, the piezoelectric actuator 1 is bonded to the housing 92, but the piezoelectric actuator 1 may be bonded to the display 91.

The casing 92 includes a box-shaped casing main body 921 having one surface opened, and a diaphragm 922 that closes the opening of the casing main body 921. The casing 92 (the casing main body 921 and the diaphragm 922) can be preferably formed using a material such as a synthetic resin having high rigidity and elastic modulus.

The peripheral edge of the diaphragm 922 is attached to the housing main body 921 via a bonding material 93 so as to vibrate. The bonding material 93 is formed of a material that is softer and easier to deform than the diaphragm 922, and has a smaller elastic modulus and rigidity such as Young's modulus, rigidity, and bulk modulus than the diaphragm 922. That is, the bonding material 93 can be deformed, and deforms more greatly than the diaphragm 922 when the same force is applied.

The bonding material 93 may be a single material or a composite made up of several members. As such a bonding material 93, for example, a double-sided tape in which an adhesive is attached to both surfaces of a base material made of a nonwoven fabric or the like can be suitably used. The thickness of the bonding material 93 is set so that the vibration is not attenuated due to being too thick, and is set to, for example, 0.1 mm to 0.6 mm. However, in the mobile terminal of the present invention, the material of the bonding material 93 is not limited, and the bonding material 93 may be formed of a material that is harder and more difficult to deform than the diaphragm 922. In some cases, a configuration without the bonding material 93 may be used.

Examples of the electronic circuit (not shown) include a circuit that processes image information displayed on the display 91 and audio information transmitted by the mobile terminal, a communication circuit, and the like. At least one of these circuits may be included, or all the circuits may be included. Further, it may be a circuit having other functions. Furthermore, you may have a some electronic circuit. The electronic circuit and the piezoelectric actuator 1 are connected by a connection wiring (not shown).

The display 91 is a display device having a function of displaying image information. For example, a known display such as a liquid crystal display, a plasma display, and an organic EL display can be suitably used. The display 91 may have an input device such as a touch panel. Further, the cover (diaphragm 922) of the display 91 may have an input device such as a touch panel. Further, the entire display 91 or a part of the display 91 may function as a diaphragm.

In addition, the portable terminal of the present invention is characterized in that the display 91 or the casing 92 generates vibration that transmits sound information through the ear cartilage or air conduction. The portable terminal of this example can transmit sound information by transmitting a vibration to the cartilage of the ear by bringing the diaphragm (display 91 or housing 92) into contact with the ear directly or via another object. That is, sound information can be transmitted by bringing a diaphragm (display 91 or housing 92) into direct or indirect contact with the ear and transmitting vibration to the cartilage of the ear. Thereby, for example, a portable terminal capable of transmitting sound information even when the surroundings are noisy can be obtained. Note that the object interposed between the diaphragm (display 91 or housing 92) and the ear may be, for example, a cover of a mobile terminal, a headphone or an earphone, and any object that can transmit vibration. Anything can be used. Further, it may be a portable terminal that transmits sound information by propagating sound generated from the diaphragm (display 91 or housing 92) in the air. Furthermore, it may be a portable terminal that transmits sound information via a plurality of routes.

Since the portable terminal of this example transmits sound information using the piezoelectric actuator 1 in which occurrence of unnecessary vibration is reduced, it can transmit high-quality sound information.

Specific examples of the piezoelectric actuator of the present invention will be described. Specifically, the piezoelectric actuator shown in FIG. 1 was manufactured as follows.

The piezoelectric element had a rectangular parallelepiped shape with a length of 23.5 mm, a width of 3.3 mm, and a thickness of 0.5 mm. The piezoelectric element has a structure in which piezoelectric layers having a thickness of 30 μm and internal electrodes are alternately stacked, and the total number of piezoelectric layers is 16. The piezoelectric layer was formed of lead zirconate titanate. As the internal electrode, an alloy of silver palladium was used.

After laminating ceramic green sheets on which a conductive paste made of silver palladium was printed, they were pressed and adhered, degreased at a predetermined temperature, and fired at 1000 ° C. to obtain a laminated sintered body.

Next, the surface electrode was printed so as to be longer by 1 mm at both ends in the width direction than the internal electrode.

A voltage with an electric field strength of 2 kV / mm was applied between the internal electrodes (between the first electrode and the second electrode) via the surface electrode to polarize the piezoelectric element.

Thereafter, a conductive adhesive containing gold-plated resin balls as conductive particles was applied and formed on the surface of the piezoelectric element to be bonded to the flexible wiring board. At this time, a conductive adhesive containing 20 vol% of conductive particles is contained in a region having a width of 0.3 mm at the peripheral edge of a region where the flexible wiring board and the piezoelectric element overlap, and 10 vol% of conductive particles are contained in an inner region thereof. The formed conductive adhesive was applied and formed.

Then, the flexible wiring board was conducted and fixed to the piezoelectric element by heating and pressurizing the flexible wiring board in contact with each other, and a piezoelectric actuator (sample No. 1) of the embodiment of the present invention was manufactured. In addition, as the above-mentioned conductive adhesive, an anisotropic conductive material that conducts in the thickness direction and does not conduct in the in-plane direction was used.

Also, as a comparative example, the above-described sample No. 1 was used except that the flexible wiring board was joined to the piezoelectric element with solder. A piezoelectric actuator (sample No. 2) outside the scope of the present invention having the same configuration as that of No. 1 was produced.

For each piezoelectric actuator, a sine wave signal having an effective value of ± 10 Vrms was applied to the piezoelectric element at a frequency of 1 kHz via a flexible wiring board, and a drive test was performed. For both 1 and 2, bending vibration having a displacement of 100 μm was obtained.

Next, when a sine wave signal having an effective value of 3 V with the frequency changed between 0.2 and 5000 Hz was input and it was confirmed whether or not abnormal vibration caused by a crack in the joint surface of the flexible wiring board occurred, the present invention was implemented. Sample No. in Example In the piezoelectric actuator No. 1, no abnormal vibration was observed other than vibration derived from resonance and anti-resonance frequency of the piezoelectric element. On the other hand, Sample No. which is outside the scope of the present invention. In the piezoelectric actuator No. 2, abnormal vibration was measured at a frequency other than vibration derived from the piezoelectric element.

Thereafter, a drive test was performed by applying a sine wave signal having an effective value of ± 10 Vrms for 100,000 cycles continuously. Sample No. which is outside the scope of the present invention. In No. 2, abnormal vibration occurred, and the flexible wiring board was peeled off from the piezoelectric element in 90,000 cycles.

On the other hand, sample No. The piezoelectric actuator 1 continued to drive without causing abnormal vibration even after 100,000 cycles. Also, no cracks or cracks were found in the conductive adhesive that connected and fixed the flexible wiring board, and no peeling of the flexible wiring board was found.

By using the piezoelectric actuator of the present invention, abnormal vibration does not occur, and even when driven for a long period of time, there is no problem that the flexible wiring board peels off from the piezoelectric element, and excellent durability is achieved. It could be confirmed.

1: Piezoelectric actuator 2: Internal electrode 21: First pole 22: Second pole 3: Piezoelectric layer 4: Laminate
41: Active part
42: Inactive part 5: Surface electrode
51: First surface electrode
52: Second surface electrode
53: Third surface electrode 6: Flexible wiring board
61: Wiring conductor
601: peripheral edge
602: Region between the outer periphery of one main surface and the surface electrode 7: Conductive adhesive
81: Diaphragm
82: Joining member
91: Display
92: Housing
921: Housing body
922: Diaphragm
93: Bonding material

Claims

A piezoelectric element comprising: a laminated body in which an internal electrode and a piezoelectric layer are laminated; and a surface electrode electrically connected to the internal electrode on one main surface of the laminated body;
A flexible wiring board having a wiring conductor electrically connected to the surface electrode and partially bonded to the one main surface via a conductive adhesive containing conductive particles and resin; The piezoelectric actuator is characterized in that more of the conductive particles are arranged in at least a part of a peripheral part in a bonding region between the flexible wiring board and the piezoelectric element than in other parts.
2. The piezoelectric actuator according to claim 1, wherein the part is in a region between an outer periphery of the one main surface and the surface electrode.
The piezoelectric actuator according to claim 1 or 2, wherein the conductive adhesive is an anisotropic conductive material.
A piezoelectric vibration device comprising: the piezoelectric actuator according to any one of claims 1 to 3; and a diaphragm bonded to the other main surface of the piezoelectric element.
The piezoelectric vibration device according to claim 4, wherein the piezoelectric actuator and the diaphragm are joined using a deformable joining member.
A piezoelectric actuator according to any one of claims 1 to 3, an electronic circuit, a display, and a housing,
A portable terminal, wherein the other main surface of the piezoelectric actuator is joined to the display or the casing.
The portable terminal according to claim 6, wherein the piezoelectric actuator and the display or the housing are joined using a deformable joining member.
The mobile terminal according to claim 6 or 7, wherein the display or the casing generates vibration that transmits sound information through cartilage or air conduction of an ear.